The appearance of electro-mechanical and other types of switches, button, knobs, and controls tends to degrade with repeated use. In addition, the appearance of physical switches and controls is generally fixed so that modifying the language or an iconic image on a physical switch or control requires replacement of the control. Moreover, it is sometimes desired to hide controls when they are not needed. Generally, this is not possible with physical controls without introducing additional structure, such as a movable panel.
Physical switches, button, knobs, and controls are useful for detecting whether a user intends to provide an input to a system. There are problems with known techniques for detecting whether a user intends to provide an input where a physical control is not present. One problem is that known techniques are expensive. There is also a problem of “false positives.” A technique may infer that some activity indicates that a user intends to provide an input, but the activity may also sometimes be consistent with a lack of user intent to provide input. When the technique detects the activity and infers intent to provide input, but the user, in fact, does not intend to provide input, the technique provides a false positive. The problem of false positives tends to become more common when known techniques are employed in an inexpensive fashion. However, low cost is important. Accordingly, there is a need for low-cost, robust methods and apparatus for detecting user input provided to a projected user interface.